A conventional spark plug typically includes a ceramic insulator body having a center electrode and an outer metal shell assembled around the insulator body and having a side electrode that is bent in an L-shape to cooperate with the center electrode to generate a spark therebetween when an electrical voltage is applied between the electrodes.
It is known to make the center electrode as a composite electrode having a copper (or copper alloy) core in an outer, oxidation-resistant nickel (or nickel alloy) sheath to improve the service life and performance of the spark plug.
In the past, the L-shaped side electrode has most often been made of nickel-base alloys and has included one end resistance butt welded to an end lip of the metal spark plug shell.
It has been proposed to make the L-shaped side electrode of the same composite material (copper core in a nickel sheath) as the center electrode to further improve the service life and performance of the spark plug. However, current production technology of copper core electrodes is limited to producing one end where the copper core is sealed in the outer sheath and an opposite end where the copper core is exposed. Since the sealed end must be positioned adjacent the center electrode, the exposed core end is all that is available for attachment to the metal spark plug shell.
Attempts to butt weld the exposed core end of the copper core side electrode to the end lip of the metal spark plug shell have been unsuccessful as a result of the presence of the exposed copper core at the butt weld joint. In particular, the exposed copper core at the weld joint provides a low resistance path for the welding current and results in a weld joint of unsatisfactory strength.
In order to butt weld the end of the copper core side electrode to the end lip of the metal shell, a substantial amount of weldable material must be provided on the end of the copper core side electrode to be welded. However, as mentioned hereinabove, current production technology of copper core electrodes is limited to producing one end where the copper core is sealed in the outer sheath and an opposite end where the copper core is exposed.
It is an object of the invention to provide a metal spark plug shell having a copper core side electrode secured in an axially extending slot in the shell in such a manner as to enable subsequent gapping of the side electrode without breakage thereof and to a method for making such a metal spark plug shell.